Epitaxial growth technique for depositing a monocrystalline film on a substrate such as a wafer is conventionally used to produce a semiconductor device such as a power device (e.g., IGBT (Insulated Gate Bipolar Transistor)) requiring a relatively thick crystalline film.
In order to produce a thick epitaxial film in high yield, a fresh source gas needs to be continuously brought into contact with the surface of a wafer while the wafer is rotated and uniformly heated. Therefore, in the case of a conventional film-forming apparatus, a film is epitaxially grown at a high speed (see, for example, Japanese Patent Application Laid-Open No. H05-152207).
In Japanese Patent Application Laid-Open Publication No. 05-152207, a ring-like susceptor supporting a wafer is fitted to a susceptor support, and the wafer is rotated according to rotation of a rotary shaft connected to the susceptor support. The susceptor has a structure that receives the outer periphery of the wafer in a counterbore created in the inner periphery of the susceptor. A mixed gas consisting of a reaction gas and a carrier gas introduced into a film-forming chamber is caused to flow radially from a central portion of an upper face of the wafer by centrifugal force due to the rotation of the wafer, and is swept out toward the outer periphery, and then discharged outside the film-forming chamber through a gas outlet.
When epitaxial growth reaction is performed in the reaction chamber, thin film created by the source gas is formed not only on the wafer but also on the susceptor supporting the wafer. If epitaxial growth reaction is performed on another wafer newly transferred into the reaction chamber, a new thin film tends to be produced on the former thin film on the susceptor, as this process continues the wafer can become stuck to the susceptor. As a result, it is difficult to transfer the wafer from the reaction chamber after the epitaxial film-forming process.
In addition, the wafer is heated to a predetermined temperature; temperature control thereof is performed during measuring the temperature of the susceptor. In this case, the temperature of the susceptor is generally known by measuring, by means of a radiation thermometer, brightness temperature of radiant light transmitted from the susceptor through a transmissive window of the film-forming chamber. However, the presence of the above-described thin film on the susceptor sometimes causes a variation in measurement result, which prevents accurate temperature measurement.
Therefore, etching is performed to remove the thin film formed on the susceptor. Such etching is performed every time a single epitaxial growth reaction is completed, or every time a predetermined number of times of epitaxial growth reactions is completed, and the thin film formed on the susceptor is removed each time. However, when the film thickness of the epitaxial film formed on the wafer increases, the film thickness of the film formed on the susceptor also increases, and the time required for etching increases accordingly. As a result, there is a problem that the time required for an epitaxial wafer manufacturing process also increases.
The present invention has been made to address the above issues. That is, an object of the present invention is to provide a film-forming apparatus and a film-forming method capable of suppressing, in the course of such a film-forming process as an epitaxial growth reaction, formation of an excess thin film around a substrate subjected to the film-forming process.
Other challenges and advantages of the present invention are apparent from the following description.